It is well known that the problem of fouling exists while burning solid fuels, such as pulverized coal, in industrial furnaces used in power stations. Contaminants deposited on the water tubes inside the furnace combustion chamber significantly reduce heat transfer in the furnace, causing a decrease in overall efficiency of the furnace and the boiler. To avoid or reduce this effect, an intensive cleaning procedure is required. Most presently used cleaning procedures involve use-intensive air blowing, which is activated in a predetermined manner in different zones of the furnace and at a predefined periodicity. Numerous attempts have been made to optimize the process of air blowing, but all of them are based on theoretical models of heat transfer in the furnace and not on the direct measurement of the thickness of the growing deposit layer. Aside from this, no real data on the reflectivity of the deposits are available; reflectivity data can provide important information about the combustion conditions and total heat balance in the boiler. Keeping in mind that up to 95% of heat transfer in furnaces originates in the radiation component, strong skepticism exists with regard to modeling results which are not based on actual reflectivity/emissivity of the furnace wall.
In order to take fouling into account in the overall balance of the boiler, it is necessary to measure two main parameters—thickness of the deposits and their emissivity—in the wavelengths of visible and infrared (IR) region. The present inventors are aware of no patent or publication that suggests a system allowing direct measurement of fouling thickness and also of fouling reflectivity in real time, at a position inside an operating furnace. Several manufacturers have used heat flux sensors for indirect estimation of fouling thermal resistance, but this approach has substantial uncertainty, since heat flux is affected simultaneously by several parameters, including some in addition to fouling thickness. Apart from this, the installation of heat flux sensors is expensive and requires replacement of a part of the wall tube and therefore needs significant maintenance efforts.
The removal of fouling deposits by air jet is referred to as “soot blowing.” Attempts to get better cleaning have led to improved efficiency of soot blowing; the use of sophisticated systems and cleaning procedures is called “intelligent soot blowing (ISB).” Existing ISB systems are based either on theoretical models of combustion and heat transfer inside the furnace or on calibration experiments. Since both approaches are predictive and not based on direct measurements, they cannot reflect variable dynamic conditions as they develop in the furnace, and therefore cannot be exploited for automatic soot blowing. To the best knowledge of the inventors, no automatic blowing system has been proposed up to now.